Why OTDR plays an important role in Fiber Testing? Why not use a economic Optical Power Meter to replace with OTDRs? Because the main advantage of using an OTDR is the single-ended test—requiring only one operator and instrument to qualify the link or find a fault in a network. And from the other perspective, OTDR gives the state of the full fiber links (OPM just give you end-point information). Operator can know fault location quickly and go there to repair it.